In an attempt to elucidate the mechanism in the induction of gynecomastia, studies of the content of androgen and estrogen in peripheral plasma and adrenal and spermatic venous effluent, as well as the peripheral plasma content of FSH and LH, will be carried out in patients with gynecomastia associated with various diseases or due to drug administration. In addition, testicular function and histology will simultaneously be studied to see if and how the hormone abnormalities are concomitantly reflected in the testes. Production and metabolic clearance rates as well as binding of the androgen and estrogen will be also investigated to elucidate the pathogenesis of any abnormalities encountered. BIBLIOGRAPHIC REFERENCES: Gabrilove J. L., Nicolis G. L., Mitty H. A. and Sohval A. R. Feminizing Interstitial Cell Tumor of the Testis: Personal Observations and a Review of the Literature. Cancer 35:1184, 1975. Sharma D. C. and Gabrilove J. L. A Study of the Adrenocortical Disorders Related to the Biosynthesis and Regulation of Steroid Hormones and their Computer Simulation. Supplementum I. Mount Sinai Journal of Medicine. Nov. - Dec. 1975.